1. Field of the Invention
The invention relates generally to improvements in steering mechanisms for motor vehicles. More specifically, the invention pertains to a modular, bolt-in, rack and pinion assembly, which has both manual and powered configurations, and which may be retrofitted to an older motor vehicle by replacing the existing steering box.
2. Description of the Prior Art
A select number of the automobiles built in years past have become collectors"" classics. For example, the muscle cars of the 1960""s, including the Ford Mustang, the Pontiac GTO, the Chevrolet Corvette, and many others of that era, have either been restored, or maintained in original condition, While these motor vehicles have classic styling and highly souand-after large displacement engines, they all share one common characteristic: their steering mechanisms display undue mechanical play, slow response, and poor centering capabilities. Rebuilding the existing steering gear boxes of these vehicles using new gears and new bearings may reduce the mechanical play somewhat, but the end result still does not approach the performance of modem steering mechanisms.
Automobile designers have long recognized the advantages of a rack and pinion construction for steering mechanisms, but their utilization in the 1960""s was generally limited to sports cars. Such a construction utilizes a bar, or rack, having teeth along one of its sides, adapted to engage with the teeth of a pinion gear. The pinion gear is connected at one end to the steering wheel shaft, and the rack is connected to the tie rods of the steering system. The circular motion of the steering wheel is converted into rectilinear motion, for translating the tie rods of the steering system.
Most rack and pinion constructions are xe2x80x9cend-drivenxe2x80x9d, in that the pinion engages a median, toothed portion of the rack, and the driven shaft portions of the rack extend outwardly, on either end of the rack housing. This results in a relatively long overall dimension, for the rack and pinion system. Another construction for a rack and pinion is termed a xe2x80x9ccenter-drivenxe2x80x9d system. In this arrangement, the pinion engages an end toothed portion of the rack, and the driven shaft portion of the rack is centrally positioned. This construction is inherently more compact than the xe2x80x9cend-drivenxe2x80x9d design.
Efforts have been made to retrofit older vehicles with more modern steering mechanisms, such as those incorporating above-described rack and pinion constructions. Unfortunately, installation of the prior art upgrade steering mechanisms have required that the frame of the older vehicle be subjected to cutting, welding, and drilling. Not only are such modifications time consuming and costly, but they are irreversible. Thus, the vehicle can never be restored to its original condition, if that be the desire of the current or a subsequent owner. The need exists, then, for a retrofit system which merely bolts into existing holes.
Further, many prior art systems, particularly those which are xe2x80x9cend-drivenxe2x80x9d, change the inner and/or outer tie-rod assemblies of the vehicle. This is necessitated by the fact that the xe2x80x9cend drivenxe2x80x9d rack and pinion is so long, that the existing tie-rods have to be replaced with shorter tie-rods. Such modifications may induce more xe2x80x9cbump steerxe2x80x9d into the steering mechanism, than existed in the unmodified vehicle. xe2x80x9cBump steerxe2x80x9d is the undesirable characteristic of the steering wheel being rotationally displaced when the wheel of the vehicle hits a bump in the road""s surface. It is desirable, then, for a retrofit system to use the existing components of the motor vehicle""s steering system to the extent possible, so as not to increase the extent of xe2x80x9cbump steerxe2x80x9d.
In addition, some car owners want a power assisted steering system, which utilizes a hydraulic pump powered by the vehicle""s engine. Others seek an upgrade to a higher performance steering system, but want to retain the direct xe2x80x9cfeedback and feelxe2x80x9d of manual steering. Prior art upgrade systems are not modular in design, so each power assisted and manual system has to be custom adapted for each vehicle. Moreover, prior art upgrade systems have no capability for fast and easy changeover, from a manual system to a powered system.
Consequently, the need exists for a high-performance steering assembly which can simply be bolted into the existing holes in the frame and control arm brackets of a vehicle, eliminating the necessity of cutting, welding, or drilling the frame or chassis.
The need also exists for a steering assembly which utilizes existing tie rod assemblies, so that xe2x80x9cbump steerxe2x80x9d will not be increased.
The need further exists for a steering assembly which is modular in design, allowing the installation either of a powered or a manual system, or a quick and easy change from one to the other.
The present invention provides a modular, bolt-in, rack and pinion assembly, of xe2x80x9ccenter-drivenxe2x80x9d design, adapted for replacing an existing steering gear box in a motor vehicle. The assembly includes a specially designed rack tube, which is readily adaptable either for manual or powered operation. The rack tube is secured to the frame and to the existing control arm brackets using brackets with split rings. The split rings are easily and quickly bolted together, circumferentially to surround the rack tube and secure it to the underside of the motor vehicle. A rack, including a tooth portion and a shaft portion, is located with the rack tube. A pinion housing is secured to a proximate end of the rack tube, with the tooth portion of the rack extending therein. A bearing, and a bushing, are respectively provided within the pinion housing and at the other end of the rack, to maintain the rack in axial alignment with the rack tube.
When the assembly is configured for powered operation, a hydraulic servo is mounted to the pinion housing. The servo has high and low pressure supply ports for interconnection to a hydraulic pump, powered by the vehicle""s engine. The hydraulic servo includes its own pinion gear, adapted to engage the tooth end of the rack. The hydraulic servo also includes output ports, respectively connected to one end of a left hand and one end of a right hand stainless steel hard line. The other ends of the hard lines are connected to a distal end of the rack tube, in spaced relation, as explained below.
The rack tube is modified for powered operation by adding certain components. A power shaft is mounted on the end of the shaft portion of the rack. A hydraulic plunger is mounted on the free end of the power shaft. An inner end plug and an outer end plug are installed in the distal end of the rack tube, defining a hydraulic chamber therein. The hydraulic plunger is positioned within the hydraulic chamber, intermediate the inner plug and the outer plug. The left hand hard line is connected to the inner plug, and the right hand hard line is connected to the outer plug, both lines being in hydraulic communication with the hydraulic chamber. Changes in relative pressure between the two lines effect right or left hand movement of the hydraulic plunger and the rack connected thereto. In effect, these modifications create a hydraulic ram which is structurally integrated within the distal end of the rack tube, and mechanically connected to the rack.
The rack tube also includes a pair of elongated slots in its sidewall, between the proximate end and the distal end. A pair of studs projects transversely from the shaft portion of the rack, each stud passing through a respective slot and a slide bushing therein. Tubular spacers are provided over the intermediate portions of the studs. The outer ends of studs are mounted to an elongated center link. The spacers maintain the center link and the shaft portion of the rack in parallel, spaced relation.
The vehicle""s factory tie rod assemblies are bolted to either end of the center link. When rotational forces are applied to the steering wheel of the vehicle, the pinion is rotated and the servo directs hydraulic fluid in the appropriate direction and pressure through the hard lines. In this manner, translational forces are applied to the rack, both through the rotated pinion and through the driven hydraulic plunger, and the tie rods are shifted in accordance with the rotational movement of the steering wheel.
In a manual embodiment of the invention, the hydraulic servo is replaced with a pinion, an outer bearing, and a dust seal. An outer, splined end of the pinion is connected directly to the lower end of the steering wheel shaft. The toothed portion of the pinion engages the rack. The hydraulic power elements, described above for the powered version of the rack tube, are not used. Thus, the previously described hard lines, power shaft, inner and outer plugs, and the hydraulic plunger are eliminated. The holes left in the rack tube by removing these components are sealed off by means of an end plug and a sidewall plug.
Using either the powered or the manual version of the rack and pinion assembly, the steering mechanism of the motor vehicle may be upgraded without any cutting, welding, or drilling of the vehicle""s body or frame. Moreover, this upgrade is accomplished without otherwise impairing the xe2x80x9cbump steerxe2x80x9d characteristics of the vehicle, from those which existed as it was originally manufactured. And, owing to the modular features of the rack and pinion assembly, the mechanism may be changed from a manual version to a powered version by adding a small number of parts, and the mechanism may be modified from left hand drive to right hand drive, by merely reversing the location of certain major components.
These and other objects and features of the present invention will become apparent in the detailed description and the accompanying drawings to follow.